*Adsorption chromatography*
The chromatographic separation of the components in a mixture by absorption from a mobile liquid stream onto the surface of a powdered solid as a stationary phase is called adorption chromatography
*Column chromatography*
It is a type of adsoprtion chromatography.
Basic principle:
The principle behind column chromatography is adsorption, in which a mixture of components dissolved in the mobile phase is introduced in to the column and the components move depending on their relative affinities.
Factors:
The experiment factor of column chromatography are (I) the nature of adsorbent ..( ii ) the nature of solvent ( iii ) the operating parameters
1.. nature of adsorbent
An adsorbent is usually a finely divided solid possessing an extremely large surface area . The characteristics of a solid that must b considered when selecting an adsorbent to effect the chromatographic seprations are ..
1 surface area ___ preferably 50m^2/g
2. Particle size 100 -200 mesh (150-75) provide a minimum resistance to flow
3. Surface activity --- higher surface activity of adsorbent will lower the separation efficiency..
2.. Nature of solvent
The solvent in which a sample is dissolved will complete with the components of the sample for surface sites upon which to b absorbed . A solvent which is strongly adsorbed in the surface will act as a strong eluent and will displace solutes easily and thus results in shorter retention time of solutes
3.. Nature of solute
The most important feature of an adsorbent chromatography separation is the extent of separation of the components of the solute sample for a given solvent adsorbent system
4.. Operating parameters.
The effect of general experimental conditions such as method of packing , flow rate and temperature are important for the effiency of a column adsorption
(a) packing
Technique if column packing is important . One common method is to pour dry powered solid slowly onto the top of the glass column . The column is gently tapped or vibrated till the solid settles
(b) Flow rate
The rate of flow rate of solvent through the column is very important in achieving successful chromatographic seprations . If the flow rate is too rapid , there will b issuffient time for the adsorption..
(c) Temperature
Increasing the temperature of the column will cause a slight decrease in the adsorption of all the components into sample . This decrease is on the order of 1-2% per degree centigrade
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